However, the exact location varies greatly. In young stems, adventitious roots often form from parenchyma between the vascular bundles. In stems with secondary growth, adventitious roots often originate in phloem parenchyma near the vascular cambium.
CK can overcome inhibition of ABA to GA – common site of actionABA cannot be overcame by GA – different site of action
INTRODUCTION• HORMONES - naturally occurring, organic substances that at low concentrations exert a profound influence in the physiological processes.
INTRODUCTION• Plant Hormones – Site of synthesis is diffused – Action at a distance is not an essential property – Response can be dependent on the sensitivity of the target cell – Multiplicity effects – Several hormones one effect
OBJECTIVES• To be able to determine the effect of various hormones in plant growth• To be able to monitor differences in plant responses
Methodology:Root FormationSuspend short stem of Coleus and place in abeaker with a part IAA and 10000 part water.Label beaker then cover.Place beaker in a sunny portion and observeresults after two weeks.
Methodology:Bud FormationRemove leaf blades of one pair of leaves at anode. Keep petiole intact.Remove the shoot tip.On one petiole apply lanolin paste on theother apply lanolin with IAA.Observe results after two weeks.
AuxinFirst described by Frits Went and first isolated by KennethThimann.It plays important roles in a number of plantactivities, including: leaf formation phototropism gravitropism apical dominance fruit development abscission root initiation and development Development of the embryo
Transport of auxin is polar.Sites of polar transport: In coleoptiles: nonvascular tissues In shoots: vasular parenchyma In the roots: xylem parenchyma (acropetal) or epidermal and cortical cells (basipetal)
Auxin stimulates adventitious root growth inexisting vascular tissues so that when they form theycan connect easily to the xylem and phloem. Adventitious roots sometimes also originate in thecallus cells that form at the cut surface this is why itpossible to grow plants from stem cuttings. Moreover, in high concentration of auxin enhancesadventitious root while inhibiting root elongation.
In shoots, auxin serves as lateral bud inhibitor meaningpresence of auxin in the stem would result to inhibition of lateral bud formation instead of stimulating growth and development. Terminal shoots inhibits later bud growth which is termed Apical dominance. Apical dominance is caused by the downward transport of auxin produced in the apical meristem. Presence of auxin in cuts would result to inhibition of lateral bud formation.
Methodology:Stem GrowthMeasure the internodes of one stem from thetip to the fifth leaf downward using a pottedColeus plant.Add one drop of GA to the apical meristemand place the plant in a sunlit area and waterregularly.Measure the internodes of the plant after twoweeks.
Gibberrellic AcidDiscovered by E. Kurosawa in 1926 through afungus in the genus Gibberrella.Some of its physiological roles in a plant are: Stimulate stem growth in dwarf plants Stimulate stem growth in rosette plants Promote seed germination Involvement in carbohydrate mobilization Promote internodes elongation
Site of synthesis: developing seeds, developing fruits, young leaves, apical region of roots Synthesized via the mevalonic acid pathwayNonpolar transport; moves in all direction in the xylem and phloem
Induce early production of seeds by somebiennials after only one season instead of two.GA does not stimulate flowering in mostplants.Addition of GA to embryoless seeds result inthe production of amylase and hydrolysis ofendosperm starch to sugar.
EFFECT OF CYTOKININAND COCONUT ENDOSPERM ON LEAF SENESCENCE
MethodologyMake 9 leaf disks from mango leavesPlace 3 leaf disks in each of three petri dishesOn the first petri dish, add distilled water. Add10% fresh coconut water on the second, andcytokinin solution on the thirdChange the solutions daily for 5 daysOn the sixth day, add 4 ml acetone and extractpigment. Check absorbance values for 663 and664nm
Results: Root Formation Petri dish Absorbance Absorbance Conc. Conc. treatment @645 (%) @663 (%) 645 663Distilled water 2.322 2.336 0.042 0.027CytokininCoconut water 2.192 2.312 0.040 0.026
CytokininFirst described by Johannes van OverbeekIt plays important roles in a number of plantactivities, including: Delaying leaf senescence Cell differentiation Cell division Promotes lateral bud growth
Cytokinin works in tandem with auxin to cause cellmorphogenesis and divisionIt is found in differentiating and meristematic parts ofthe plantTransport is non-polarSite of synthesis: root tipSynthesized by condensation of isopentenyl groupgroup of DMPP with 6 nitrogen of ADP and ATP
Desiccation of the cells of the first set up wasuninhibitedFor the other two set ups which have exogenoussupply of cytokinin, senescence was delayedCoconut water has cytokinin which the seed useswhen it germinates
Methodology • Get two healthy potted Coleus plants • Place a cut apple in one pot • Water plants and cover both in black plastic bags
• Leave for around 3 days• Observe coloration differences and general appearances• Using spectrophotometer obtain the chlorophyll content of leaves
Results Chlorophyll content of leaves Sample Chlorophyll concentration (umol/ml) 645 nm (Chl B) 663 nm (Chl A) A (without 2.83 2.94 ethylene)B (with ethylene) 2.3 2.9
Ethylene• Ripening fruit is a source of of ethylene• Causes changes in fruit as it ripens• Breakdown of chlorophyll, synthesis of other pigments• Softening due to cellulase and pectinase• Converts starch and acids to sugars• Disappearance of phenolicslike tannin
Enhances rate of senescence• Senescence is the programmed aging process leading to death• From genetic programming or hormonally induced• Aging is associated with the loss of chlorophyll as leaves fade or turn brown.
• Chlorophyllase breaks down chlorophyll• Can also control abscission depending on the balance with auxin
EFFECT OF VARIOUSGROWTH REGULATOR ONSEED GERMINATION
METHODOLOGY WATER WATERABA GA ABA ABA, GA,CK CK, GA CK
resultsTreatment % germinationGA, dark 26.6CK, dark 95ABA, dark 0ABA, light 1.3GA, CK, dark 26.6GA, CK, ABA, dark 0H20, dark 95H20, light 98
DISCUSSION• Actions of GA, CK, and ABA are mediated directly or indirectly via protein synthesis (Fountain and Bewly, 1976)• Gibberellic acid - the hormone that promotes seed germination by initiating the synthesis of amylase which the seeds require to break down and hydrolyze endosperm to sugar – their source of nutrition
DISCUSSION• Cytokinin - promotes cell division and morphogenesis of the seeds• Abscisic Acid - the hormone t hat regulates the germination of the seed, signaling its maturity; ceases the growth of the seeds, but serves as the sink for nutrients
DISCUSSION• Water: Light or Dark – requirement for germination of lettuce seeds – Control• Lettuce seeds – require light and cool places for its germination – Therefore, light wins!• Why dark? – To isolate the sole reaction of seed germination due to GA, CK and ABA without the aid of light that might trigger other hormones
DISCUSSION• ABA in Dark – ABA: inhibitory hormone for seed germination – Dark: not suitable location for lettuce seed germination – Therefore: least germination• ABA in Light – ABA: inhibitory hormone for seed germination – Light: promotes germination of lettuce seed – Therefore: relatively more % germination than ABA in Dark
DISCUSSION• GA in Dark – GA: promotes seed germination by break down of starch to glucose via generation of amylase – Dark: not suitable location for lettuce seed germination• CK in Dark – CK: promotes seed germination by cell division and morphogenesis – Dark: not suitable location for lettuce seed germination * Therefore: germination will still occur in both
DISCUSSION• GA and CK in Dark – GA: promotes seed germination by break down of starch to glucose via generation of amylase – CK: promotes seed germination by cell division and morphogenesis – Dark: not suitable location for lettuce seed germination – Both GA and CK promote seed germination – Therefore: more % germination than in GA or CK alone
DISCUSSION• GA, CK and ABA in Dark – GA: promotes seed germination by break down of starch to glucose via generation of amylase – CK: promotes seed germination by cell division and morphogenesis – ABA: inhibitory hormone for seed germination; antagonistic to GA – Dark: not suitable location for lettuce seed germination – GA and ABA cancel out, CK remains – Therefore: there will still be % germination but less than the GA and CK combined, and approximately same as CK alone.
conclusion• % germination:Water in light > GA and CK in dark > GA in dark = CK in dark = GA, CK, ABA in dark > ABA in light > water in dark > ABA in dark
CONCLUSION• To be able to determine the effect of various hormones in plant growth• IAA – promote adventitious root formation; inhibits bud formation• GA – promote elongation of stem internode• CK – delay leaf senescence• Ethylene – promote leaf abscission
CONCLUSION• To be able to monitor differences in plant responses• As seen in the experiment, plant respond differently to different hormones – Formation of adventitious roots – Inhibition of bud formation – Elongation of internodes – Leaf senescence and abscission – Seed germination